1. Technical Field
The present invention relates in general to perpendicular recording media for hard disk drives and, in particular, to an improved system, method, and apparatus for fabricating soft magnetic film with preferred uniaxial anisotropy for perpendicular recording.
2. Description of the Related Art
In perpendicular recording media, the soft magnetic underlayer (SUL) film gets thinner as the write pole head gets smaller with increasing areal density. An anti-parallel (AP) coupled SUL structure (e.g., two SULs separated by an Ru spacer) is widely used in disk drives because of its remnant state of cancelled magnetic moments between the two SULs. Uniaxial anisotropy of the SUL is induced by a radial cathode magnetic field during sputter deposition. The cathode field strength should be higher than the AP exchange field, Hex, in order to induce radial anisotropy.
As for the second SUL deposited onto the Ru spacer, the initial deposited layer experiences a very high AP exchange field having a direction opposite to the cathode field direction. Moreover, its anisotropy direction (i.e., the magnetic easy axis) can be tilted out of the radial direction or rotated into a circumferential direction if the Hex is strong enough to exceed the radial cathode field. As the layer gets thicker, the Hex decreases sharply and then the cathode field can readily overcome the Hex to align the anisotropy to the radial direction. Inducing radial anisotropy in an AP-coupled SUL becomes an issue as the SUL thickness decreases.
As shown in FIG. 1, for a SUL (Bs=1.2 T) thickness below about 12 nm, the Hex 11 is higher than the cathode field (e.g., about 60 Oe), which makes it difficult to align the radial anisotropy of the top SUL. In this case, the dispersion of the second SUL anisotropy is observed due to interference between the cathode field and the Hex. However, as a result of this, the saturation field 21 (FIG. 2) of the SUL in the circumferential direction is reduced. Thus, an improved solution for fabricating soft magnetic film with preferred uniaxial anisotropy for perpendicular recording would be desirable.